Report

Dordrecht, 4 September, 2005 - After a successful test with a 12.5mm throat (CMT0505) the discussion started of what the throat of the next test motor was to be. The most logical choice was 12mm, but we have already had two failed motor tests with a 12mm throat (CMT0409 at NLD20 and CMT0410) where the safety mechanism was activated because the pressure inside the motor was to high. However the results are questionable when compared against the results of CMT0503 at NLD21 (P_max: 1512kPa) and CMT0505 (P_max ca.: 2000kPa), which is well below the projected 4000kPa. Using these last two results as a start for some well thought through guessing, the pressure of a similar test motor with 12mm throat should be well below the 7500kPa at which the safety mechanism was set at the earlier tests with a 12mm throat. It should even be below the 4000kPa.
It was decided to do the test with a 12mm throat.

On the sunny afternoon of Sunday 4 September we did the motor test. Although some predicted the same result as the earlier motor test with a 12mm throat, all went very well this time. The P_max of ca. 2600kPa was even a bit disappointing.

The discussions of what to do to get more pressure at the next motor test started right after the results were read just after test. After a week the proposed course of action was to lower the number of grains in the motor from seven to six, but retaining the overall length of the motor by increasing the length of the grains longer from 80mm to 93mm. We are not sure yet if we already want to decrease the throat diameter to 11.5mm, because then we cannot compare the results of the six to the seven grains test motor.